A saccular aneurysm of an azygos anterior cerebral artery: A rare anatomical variation and review of literature

Ankur Bhupendrakumar Pachani; Jaimin K Shah; Sachin V Bhimani; Shailendra J Solanki

doi:10.4103/jmgims.jmgims_51_16

CASE REPORT

Year : 2018 | Volume : 23 | Issue : 1 | Page : 43-45

A saccular aneurysm of an azygos anterior cerebral artery: A rare anatomical variation and review of literature

Ankur Bhupendrakumar Pachani, Jaimin K Shah, Sachin V Bhimani, Shailendra J Solanki
Department of Neurosurgery, B. J. Medical College and Civil Hospital, Ahmedabad, Gujarat, India

Date of Web Publication

3-Apr-2018

Correspondence Address:
Dr. Ankur Bhupendrakumar Pachani
Department of Neurosurgery, B. J. Medical College and Civil Hospital, F5 - NCT OT, 2nd Floor, Ahmedabad - 380 016, Gujarat
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jmgims.jmgims_51_16

Abstract

The azygos anterior cerebral artery (ACA) is a rare variation in the circle of Willis. Azygos ACAs often associated with other vascular or nonvascular anomalies. These aneurysms can be noninvasively imaged either by conventional computed tomography (CT) angiography or magnetic resonance angiography, but digital subtraction angiography is the gold standard for diagnosis. We report a case of saccular aneurysm of azygos ACA, diagnosed by multidetector CT cerebral angiography and treated by craniotomy and clipping of aneurysm. The clinical significance of the rare anomaly is highlighted. We report this rare clinical experience with review of the literature.

Keywords: Anatomical variation, azygos anterior cerebral artery, rare anomaly, saccular aneurysm

How to cite this article:
Pachani AB, Shah JK, Bhimani SV, Solanki SJ. A saccular aneurysm of an azygos anterior cerebral artery: A rare anatomical variation and review of literature. J Mahatma Gandhi Inst Med Sci 2018;23:43-5

How to cite this URL:
Pachani AB, Shah JK, Bhimani SV, Solanki SJ. A saccular aneurysm of an azygos anterior cerebral artery: A rare anatomical variation and review of literature. J Mahatma Gandhi Inst Med Sci [serial online] 2018 [cited 2023 Mar 30];23:43-5. Available from: https://www.jmgims.co.in/text.asp?2018/23/1/43/229156

Introduction

The azygos anterior cerebral artery (ACA) is a rare variation in the circle of Willis with an extremely low incidence of about 0.1%–5%, in which the distal (A2) segments of both ACAs are represented by a single common vessel, from which arise all the major vessels supplying most of the medial aspect of both anterior cerebral hemispheres and the corpus callosum.^[1] As a variant of normal embryogenesis, azygos ACAs often associated with other vascular or nonvascular anomalies such as agenesis of corpus callosum, porencephalic cysts, hydranencephaly, saccular aneurysms, and arteriovenous malformations.^[2] Indeed, saccular aneurysms of the azygos or unpaired ACA are more frequent than previously estimated. Its occurrence rate has been reported to be between 13% to 71%.^{[1],[2],[3],[4]} However, only a few cases have been reported in the literature. We report a case of saccular aneurysm of azygos ACA, diagnosed by multidetector computed tomography (MDCT) cerebral angiography and treated by craniotomy and clipping of aneurysm. The clinical significance of the rare anomaly is highlighted.

Case Report

A 40-year-old male patient presented to the emergency department with the sudden onset of a bifrontal headache, dizziness, and drowsiness. On neurological examination, he showed drowsy mental status, mild left upper, and lower limb weakness and did not display any other neurological focal signs. Computerized tomography scan of brain showed evidence of bleed in the right frontal region with extension into both lateral ventricles, a subarachnoid hemorrhage in a basal cistern with no evidence of hydrocephalus [Figure 1]. MDCT Cerebral angiogram showed both A1 segments join to form a single ACA (Azygos ACA). A wide neck saccular aneurysm pointing anteriorly was noted at the distal end of A2 segment and distal azygos ACA then divides into two branches [Figure 2]. Three-dimensional computerized cerebral angiogram showed distal azygos ACA pointing anteriorly [Figure 3]. He underwent craniotomy and clipping of a saccular aneurysm arising at distal azygos ACA. The procedure was uneventful. Postoperative MDCT Cerebral angiogram showed clipped aneurysm with postoperative changes without evidence of any infarct [Figure 4].

Figure 1: Computed tomography brain plain showing evidence of bleed in the right frontal region with extension into both lateral ventricles

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Figure 2: Multidetector computed tomography cerebral angiogram showing saccular azygos anterior cerebral artery aneurysm

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Figure 3: Three-dimensional Computerized angiogram showing (a) distal azygos anterior cerebral artery saccular aneurysm (b) pointing anteriorly

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Figure 4: Postsurgery multidetector computed tomography cerebral angiogram showing (a) clipped saccular azygos anterior cerebral artery aneurysm (b) with postoperative changes or without any infarct

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Discussion

Wilders in 1885 described arteria termatica, the formation of one artery from the fusion of the A2 in the ACA. He called it the azygos artery of the pericallosal artery. In 18-mm embryos the ACA takes a medial course. Four days later, the arteria communicans anterior develops from the anterior plexus. ACAs run in a rostro-occipital direction with the development of the corpus callosum. The unusual fusion of paired postcommunicant segments of ACA originates either from the medial branch of the olfactory artery at the initial 16-mm stage of embryogenesis or the persistence of the median artery in the corpus callosum at the 20–24 mm stage. It can also be generated by a lack of development or regression of the ACA.^[5]

The ACA and anterior communicating artery (AComA) complex are an important division of the circle of Willis. The AComA has shown many types of anomalous structures: plexiform (33%), dimple (33%), fenestration (21%), duplication (18%), string (18%), fusion (12%), median artery of the corpus callosum (6%), and azygous ACA (0.3%–3%).^[6] Variation of ACA deserves attention because they regulate the distribution of blood to both the cerebral hemispheres and certain clinical syndromes of cerebral vascular occlusive disease will be a function of their specific anatomic structure. Thus, they have a significant impact on the arterial hemodynamics of the frontal lobe.

As per Baptista's review of the literature, 23 of 2153 adults (1%) had azygos ACAs. He described three types of anomalies in the distal ACA as follows: (a) A true azygos artery, from which all major branches are given off to both the anterior cerebral hemispheres; (b) A bihemispheric ACA, where both right and left ACAs are present, but one is rudimentary and most of the major branches to both the hemisphere arise from the other ACA; (c) A triple ACA, with the accessory ACA arising from the AComA. Our case belongs to type (a).

Although azygos ACA are rare in the healthy population, aneurysms coupled with azygos ACA are not uncommon due to increasing hemodynamic stress. An azygos ACA has twice the blood flow and hemodynamic pressure of a normally paired A2 region of the ACA, which increase its susceptibility to aneurysm formation. The development of an azygos ACA a saccular aneurysm is associated with blood flow restriction and pressure on the arterial wall in the distal portion of the parent artery.^[1] Hashimoto et al. proved this hypothesis by their experimentally induced aneurysms.^[7] However, not all aneurysms develop at the increased impingement site. Few authors have mentioned the unclear role of increased hemodynamic stress. Pathological vascular wall structure might also cause the development of the aneurysm since embryo. The existence of an aneurysm was considered to be a congenital defect in the tunica media, and hemodynamic stress applied in this area can produce aneurysm formation and growth.^[3]

The clinical significance of azygos ACA is threefold: (a) Its association with other congenital malformations; (b) The existence of an azygos ACA can explain the presence of bilateral ischemic changes in the setting of occlusion of the vessel and; (c) The high incidence of associated berry aneurysms.^[8] In our case, other than the aneurysms, no other central nervous system malformations were detected.

These aneurysms can be noninvasively imaged either by conventional CT angiography or angiography, but digital subtraction angiography plays an important role in identifying the saccular aneurysms of the azygos ACA, and it is the gold standard for diagnosis.^[9] An exact diagnosis is important because extra precaution has to be taken during the treatment of these aneurysms since the injury to this common arterial trunk can lead to devastating complications.^[10]

Conclusion

Although the incidence of azygos ACA is a rare but saccular aneurysm of azygos ACA is not uncommon. Conventional angiography should be examined carefully to avoid missing the diagnosis, to evaluate the form and projection of aneurysm and to detect other associated vascular anomaly. Extra precaution has to be taken during the treatment of these aneurysms since the injury to this common arterial trunk can lead to devastating complications.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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